The present invention relates to a method of driving piezoelectric devices fitted with piezoelectric films having a perovskite-type crystal structure represented by the general formula Pb(Tix,Zry,Mz)O3; in particular, the present invention relates to a method of driving such piezoelectric devices in a way that improves their durability.
In recent years, active R&D efforts are being directed to various kinds of devices that use the piezoelectric element, as exemplified by actuators, sensors and memory devices, and piezoelectric films that are formed by vapor-phase growth techniques such as sputtering are drawing particular attention as functional films capable of high performance. Such piezoelectric films are currently used in piezoelectric devices such as piezoelectric actuators in ink-jet heads, micro-pumps and so forth.
JP 5-338150 A discloses an ink-jet head and a method of driving it; in the ink-jet head, an electric pulse is applied to a piezoelectric material to cause partial deformation of an ink chamber, whereupon a pressure pulse is generated within the ink chamber so that an ink drop is ejected from a nozzle. According to JP 5-338150 A, the application of the electric pulse that causes ejection of an ink drop is followed by the application of an additional electric pulse that produces a voltage of opposite polarity with respect to the first applied electric pulse, whereby the ink meniscus is rapidly reverted to the reference state so that the response frequency of the ink-jet head is sufficiently increased to enable faster marking.
JP 6-342946 A discloses a method of regenerating a piezoelectric device which is characterized in that in order to restore the displacement performance of a piezoelectric device that has deteriorated in that performance due to prolonged use, an electric field at least equal to the coercive electric field is applied to the piezoelectric device in opposite direction with respect to the electric field applied during the drive mode. According to JP 6-342946 A, the disclosed method of regenerating a piezoelectric device is such that the piezoelectric device, namely, a piezoelectric film that has been driven for a prolonged time to have an internal electric field formed in it is supplied with an electric field at least equal to the coercive electric field of the piezoelectric film in opposite direction with respect to the electric field applied during the drive mode, whereupon the internal electric field is destroyed to restore the displacement performance of the piezoelectric film.